The preferred embodiment relates to a flow adjustment apparatus including an actuator and a valve actuated thereby.
The actuator which in the field of process engineering, nuclear power systems, petrochemical plants or the like, may be configured as a pneumatic actuator, for example, features an actuating rod which is translationally displaced to perform as a lift actuator. The actuating rod extends up to the valve and ends in a valve member which is traveled to close or open a valve seat in the passage of a fluid line.
Many types of flow adjustment apparatuses need to satisfy extremely stringent safety regulations. For example, emergency OFF valves or emergency shut down valves are required to attain an emergency position with exceptionally high reliability in which the valve member fully opens or closes the valve seat when the plant develops a fault.
A generic flow adjustment apparatus is known from U.S. Pat. No. 6,905,108 B2 which features a pneumatic linear actuator of lift actuator with a travel limiting device intended to prevent over-travel of the actuating rod of the actuator particularly when the lift actuator is fully actuated pneumatically. The travel limiting device is achieved by two collar halves of a two-piece collar each including serrations on an interior surface shaped and sized to mate with actuating rod serrations disposed on the valve actuating rod. By releasing two setscrews interconnecting the two collar halves secure to the actuating rod, the position of the travel limiting device can be set relative to the outer wall of the actuator housing acting as a stopper in thus limiting the travel of the actuating rod.
It has been discovered that assembling this known flow adjustment apparatus is a major problem when the actuating rod of the actuator together with the valve member needs to be inserted in the valve housing. In addition to this, locating the travel limiting device freely accessible on the outside of the actuating rod has proven to be a source of potential malfunctioning since, especially in faulty operation of the plant, objects can become lodged between the travel limiting device and the stopper wall of the housing, resulting in an unwanted change in limiting the travel. But the main disadvantage experienced with this known version of the flow adjustment apparatus is its highly complicated assembly when it is to be retrofitted by replacing the actuator without detrimenting the valve structure.